Cutter for producing gears



Jan. 1, 1946. E. WILEIJHABER Q 2,392,278

CUTTER FOR PRCDUC ING I GEARS Filed Jan. 19, 1942 7 Sheets-Sheet l F 4 l By 5 Zmnentor ERNEST W/LDHHBER Jan. 1, 1946. E. WILI DHABER 2,392,278

' CUTTER FOR PRODUCING GEARS Filed Jan. 19, 1942 7 Sheets-Sheet 2 90 9/ 92 a; 24 95 9a 97 9a 99 x00 /0/ m2 m3 m4 m5 ma /07 m 709 Fla ' 5/ I Z'mventor [KNEST W/LDHHBER (Ittomeg Jan. 1, 1946. E, WILDHABER 2,392,278

CUTTER FOR PRODUCING GEARS Filed Jan. 19, 1942 7 Sheets-Sheet 5 Q I Snoeptor ERNEST W/LDHHBER Jan. 1, 1946. v E. WILDHABER 2,392,278

CUTTER FOR PRODUCING GEARS '3maengor EE/V ES'T w/w/mam Fly .16 3% (Ittorneg Jan. 1, 1946.

/36 E456 l III E. WILDHABER CUTTER FOR PRODUCING GEARS Filed Jan. 19, 1942 '7 Sheets-Sheet 5 F y Z1 3nnentor Jan. 1, 1946. wlLDHABER 2,392,278

CUTTER FOR PRODUCING GEARS Filed Jan. 19, 1942 '7 Sheets-Sheet 6 v .Flg )ZB 3nventor fk/vzsr wan/mark Jan. 1, 1946. 2 E. WILDHABEIVQ' 2,392,278

CUTTER FOR PRODUCING GEARS Filed Jan. 19, 1942 7 Sheets-Sheet '7 Enventor $12 4 56 ERA/E57 WILDHHIBER 4 Egsb F3455- across the face of theibla'n' aiidii Patented Jan. 1, 1946 v OFFICE 2,392,278 m curifififibkfnonncme GEARS Ern'st wilahatemnii mom; Ni assignor to Gleason worksg Rochester; N: 16.,- a corporation of New York AfiilicaZtion-Janiiirim, 1942;'s i-'1 t1\iu. 427;323- 21 -Gl'aiins. (01. 2911- 103);

The. present; inve tion :jla'tes w gutters for anew nietliod's of "producing, gears, and par ion 1am to disc-type ciitters wmen are offiiarying point-width aroundtlieiiperiphery andto metliod's ofiemployingfsuch ci i'tters'in'thefpfodi ction omraiglifi tootheynii eal andtapra gears;

In'my pending applications, s'rial'n sl- 3,6 '43? and 401,631, filed. ojetokieigs; 1940'; a ziQQJiily: 9', 1941 respectively, new Patent? No. 21357 153 .of August. 2?),v 19, 111 arid v 61,2137eg4s5" ofM zz', o th f: utt?rs--1iereto 0 m oyed l945lrespectiiielii; 1 have desoribeqmeth of esses-s cutting" bevel gears" which age-type mill ng A further object o; the inyentionu sjt cutters are erhplo y ed that have: mads qfym porate" the principles" of the irfventuon ingdpoint f-width andefiectii' cofitoursf ofcliang construction of a cu tter pay b e nsedi for mgjprom enapeamundimeirperipher es-anew rgl e r gan; PQI' IQYl BfE'FQWLEP which'eacli-tootl i spaceoffagear'blaiiknot"? 3 1 49? fis 'ef C l 1$f ears m!) 7 rotating .theclitterifl rigag'rne "t with the blank s'uchwciltter; While eif'ctiiig 'va; remtive' e'rig thwis reed move- Other ohi fi 9 the ny nti wi l eep merit" betw enmhe tter nd 'lank a k; n 6111: fron'i'the 'sp" cincation an cl fro'mwhe recital forth acros the face of'tlie" blank in time with the 'ciit'tei rotatiori'sothat difirentbladesd ctittei 'c'ut' atdifirht-pointsialong h'e1ngt t pnmha blde 9 Yeoman etzwiq .{h a tooth space dfiring a r'voliition'of the c ter qfiifojrfl" ht; an heiritip"-' tinge are to preoduceva tooth space tapering iqwidthljfrxh en aged-ma end to eridaIs' required inia besfel-"gearl In my cu'tterp pend vanp b i i No; 6w! ft i m; ployedgi 'orjthe gamype 'nf nasib mrdugh jg a dnishing blades sothat a tootn spa'ed f a gear blank-maybe successivelyroughed an'a finished in a pa'ss'of thacuttn bac emf-forth 3 I a; .gl'e r-eir olutioni of the'cutteri. Ifi't e'meth'od'of' lnyiapplication'N'o. 401, 31, the cutter; akes seyral asses back and rormacrosg the f'ace 'of the blank in the course of cutting atooth space, beingliid relatively into depth between" or during pas ses until full tooth depth is reached, ancl thenfbeing withdrawnfrofirengagement withfl th -blan to permit indexing tlidbl'ank': Thi latter'applipa tion preferab1y employs a *ciittei having v blades 40 all around its periphery and is eepecianysuitable for-:rough-cutting:operations; V The cutters used in"my" two applications-menitioned area-quite similar a, in structure 'and' an aim ofathepresent-invention-.genera11y:is to provide improvements that will be applicable to cutters use ci in;bothprocesses; r V v v Ap i a y-Q iec of -them ent nt mi t provide. d SQ-P p tt r s fiab e or. cu in gears accordingto the-process of x my application N6. 4 01;63'1Qab ov'e mentione d, which will" be simple'anc'l'as ytofmake} I V v p Ajf orther object ofitH invention is"toipioviiie 20 of"ti efabp ndfl inis Cuttersma'de according to th width, cut at least depth, while those which ar of least point width, cut at full depth.

The blades of the cutter can all be made with straight sides perpendicular to the axis of the cutter, that is, of zero pressure angle, or with sides that are curved. blades may be made of less height than the height of the tooth spacesto'becut so as to obtain addition to'a maximum number of cutting edges and longer life, tooth shapes as closely aspos- In either instance, the

sible approximating the finished tooth shapes I desired. Blades of cutters constructed according to the present invention may be made up in several stock sizes in advance and ground to the precise desired curvature when required. Thus manufacturing costs may be reduced to a minimum.

Several difierent embodiment of the invention are illustrated in the accompanying drawings, in which:

Figs. 1 to '3'inclusive are. diagrammatic views, showing successive longitudinal positions of a cutter, when in full depth engagement with a gear blank,-in the process of cutting gears according to thermethod of my prior application No. 401,631;.

Fig. 4 is a'plan viewand Fig. 5 a diametric sectional view of a cutter constructed according to one embodiment of this invention and suitable for use in the process of my tion No. 401,631; -Fig. 6 is a developed sectional view of this cutter; V 1 Fig, 7 is a diagrammatic view, illustrating the prior applicarelationship between the cutter and the blank when the cutter is at the middle of its stroke in full depth position; I Fig. 8 isa diagrammatic view, showing one 'way in which the profile shapes of the side:

cutting edges of the blades of this cutter may be determined; 1

. Fig. 9 is a further diagrammatic view, showing in greater detail the kinematic relationships existing between the cutter and the blank, and further illustrating how the profile shapes of the side-cutting edges of the blades of the cutter may be determined; w a

Fig. 10 is a section through cutter and blank taken through a mean point longitudinally of .thetooth space of the blank at right angles to line 69;

Fig. 11 is a diagrammaticview illustrating the positions occupied by diiferent blades of the cutterdurin the-cutting of a tooth of the blank;

Fig. 12 is a diagrammatic view, showing the different blades superimposed on one another in a radial plane of the cutter; V Fig. 13 is.a diagrammatic view illustrating one way of producing the radial feedmotion of the cutter in manufacture of the cutter;

Figs.,14 and 15 are diagrammatic plan and posed on one another in a radial plane of the cutter;

is a developed sectional view of this cutter;

Fig. 21 is a diagrammatic view looking at the end of a tooth space of a spur gear and showing how a modified form of cutter made according to this invention maybe used, to 'cut this gear; Fig. 22 is a diagrammatic view, showing several of the blades of this last form of cutter superimposed on one another in a radial plane of the cutter;

Fig. 23 is a developed sectional view of this last form of cutter;

Fig. '24. is a diagrammatic view, illustrating a method of cutting bevel gears according to this invention in which the cutter has a feed in one direction'lengthwise of a tooth space; V

Fig. 25 is a diagrammatic view, showing, superimposed on one another, several blades of a. modified form of cutter constructed according to this invention which is adapted to be used in the method illustrated in Fig. '24; v

Fig. 26 is a diagrammatic view, illustrating a further modified method of cutting bevel gears according to this invention with a lengthwise feed of the cutter in one direction;

. Fig-2'7. is a diagrammatic view showing one way of cutting the tooth surfaces of a bevel gear according to this invention where .the' cutter is fed first in one direction and then in the opposite direction longitudinally of a tooth space;

Fig. 28 is a diagrammatic view, showing the angles through which the cutter rotates during the different parts of the cycle of cutting a tooth space by the process disclosed in Fig. 27;

Fig. 29 is a diagrammatic view showing a still further method of cutting bevel gears according to. this invention in which a tooth space is roughed by movement of the cutter longitudinally of the tooth space in' one direction and finished on the return feed movement of the cutter; I

Fig. 30 is a diagrammatic view, showing the angles through which the cutter rotates during the different parts of the cycle of cutting a tooth space according to the method shown in Fig. 29;

' Fig. 31' is a diagrammatic view, illustrating a sectional views, respectively, showing one way of relieving the side surfaces of blades of the cutter shown in Figs. 4 and 5;

Fig. 16 is a plan view of a diiferent embodi ment of a cutter made according to the present invention; I I

Fig. 17 isafragmentary diagrammatic View, looking at the side of a toothjspace andFig. 18 is a fragmentary diagrammatic view, looking'at the end of a tooth space, and showing how the cutter of Fig. 1 6 may be employediin the cutting of a spur gear according to the present invention;

.. Fig. 19 is a fragmentary diagrammatic view, f

' showing several blades of this cutter superimfurther modified process of cutting bevel gears of one of the-seg in. a process in which the cutter is rotated in engagement with the gear blank while simultaneously a relative feed movement is produced between the outter and blank in time with the cutter rotation. The feed movement may be a movement lengthwise of a tooth spaoeof the gear blank, or a movement depthwise, 'or it may be a combination or both lengthwise and depthwise movements. Figs. 4 and 5 showa cutter made according to this inventionlfor cutting gears according to the process of my prior application No.

401,631 above mentioned where-both lengthwise:

, l "lit il'jiise' ovements re produced} in th the c utterrotatidn, t, s

cutter of Fi s. 4% an 5- piiira i' 'r' or radians-arranged inserted blades 50 which e secured in slots .provid ed around the periphery of the rotary cutter head 51. The blades are secured to the cutter headby screws '52 and a Clamping disc 53. The blades 50 are relieve both on, their tips and sides back of their front faces to have tip and side-cutting edges. The sidecutting edges of the blades are of curvedprofile, preferably being concave eir'cul'ararcs. The profile. curvature of correspgi ing side cutting edges of thejblades is preferably uniform, but the centfrs of curvaturelo'f the corresponding side-edges of successive blades are preferably displaced from orie ano her, as w l e d scribe h e fter j i deta l. The bladesalsjo have progressively varying point width, as will be described in further detail hereafter.

In the instance illustrated, the blades are double-edged, being sharpened so that each blade two side-cutting edges, respectively, at opposite sides of the blades. It will be understood, though, that the blades might be sharpened instead to have side cuttihg edges for cutting'on one" side only 'of a tooth space, and alternate blades might then be sharpened to have opposite side-cutting ed es. i

ri s; 1 to ,3 inc isiv illus te d ag m atically the method of m'yapplication No. 401,631, showing different successive longitudinal positions 6f the cutter c a l-ter it has' been fed into full depth position. 51 denotes the gear to be cut, 58' its axis, and 59 its apex. As the cutter rotates on its axis 54, it is simultaneously fed lengthwise of the tooth space being cut in time with its rotation, the axis 54 moving along a line "55 which is parallel to the root line 55 of the tooth space being cut. Fig. 1 shows the position tithe cutter when it is cutting fat the small end of the tooth space 'of the bevel gear 51. Fig. 2 shows the position of the cutter after it has rotated angularly and has been fe'dlongitudinally from the position shown in 1 and is cutting at'th center of the tooth space of the gear, While Fig. .3 shows the position of the cutter whfen it .iotated thisiigh a still further. angie and "has 'ben'fied further along the length of the tooth space and is cutting at the large end ofthe tooth space.

In the process of my application ,No. {101,63

the lengthwise ir'io'v ment of the cutter is pref- 'I'rably produced by mounting the cutter eccentri- 'ii'tlly on the tool spindle of the machine'and' roimovement takes place during a plurality .ofrevolutionsof the cutterand mar ne controlled by ea er-iii;able ,feed cam. After a tooth space of the blank has been cut, the cutter is withdrawn from engagement with the blank, the blank is indexed,

and the cycle begins anew.

i Fig. 7 shows a cutter operating according to the process of my application No. 401,631 in the middleot its lengthwisefeed stroke and at full depth position. The cutting surface of the (cuttier, that is, the surfacewhich contains an or its sittin s me s c nt s s w h: theic i r ac Broducedbn the gear b1a'nk'51' alonga 'line 60 Mei: is his t rnin angle of th G i ter which extends somewhat diagonally semis the tooth side.

As already stated, in the movement of the cutter at full depth, the cutter center un avels 1!} the direction of the root lineifi or the gear-mask 51. The cuttercenten then travels between the e d positi n 5.4 nd 4- Becau e 9t he ha i 'nic' mot on. o he u er due. o ts' c enfiric mo n ma. the. e ot f n th Se movemen or the t r s a a. max m ma the center o e stro nd ze o its. ends Where r verie! occur In ny interm at si i n 54 or inat 541* is a m asure o the ins a 011$ v c y. r the ut r cente in; i i s- Th point 6. islq ate on a circle 6 draws she the center 54 of the cutter through the Po 54 nd '4"- Thsanlsle 0, whi h s squar ng o t r c nt m es o he posi ion 54;

p sition 5 It will be n that the Q l d to t e rig t. the mi 54 i p tional to sin a and t at the in staii n ta s;

ity is proportional to cos 6.

Insetting out to make a bevel gear cutterfo'r practicing the process of my application No. 401,631, the first task before us is to determine the cutting surface required to cut a given bevel gear. As will be seen from Figs. 9 and 10, the tangents and 65. to opposite sides 56 and 66 of a tooth space of the bevel gear 51 at meanpoints 61 and 67 are seen to intersect in a point- 68: The tangential planes to the tooth sides atithe points 61 onta nt e sa d t n entsfii an and also pass through the pes 59 0f 'thelbeycl gear. i' I'l'iey intersecttherefore, in a i ifi e ich nne s the ape .5 with w rm??? and which is e e d cular to the draw sp en of 10. These tangential planes contact} mgteover, with the tooth suiiacss o t e b vel gear a O a st aig t li n iaa si ns'imm h es-e 59 a d assin t r u h t m an paint s1 and'B'l. I

Let us now analyze the location of the ppii'its of the cutting surface whichare conjugate to the straight line of tangency '10, whey 'arelpeifnts which during rotatioh and lengthwise feed bfit he cutter will describe said straightline,

v I have found that the cutter surface copjj igate to a tangential plane 6l-59- i58lis a con absurface centered at 15 (Fig. 9) and havi gia n ax is parallel to and offset from the center 34 of the cutter. This conical surface describes the entire tangential, plane 6'|,s59x. 6S, within the ilehgth of a tooth side; during the relativeirotational and lengthwise feed movement of the cutter and, therefore, also contains the sought curve.

In the position shown in Fig. 9, and in any other position, a tangential plane contacts with its conjugate conical surface in a traigh line which is the pr e n of h in t ntaneous axi of." .la-

tive motion to fsai'dpla'ne. ihnig. 9, thi e ght use passes through the instantaneous axis 162' and mean pointin -and coincides with the tanse t as (Fis- 10 e he cute has a 541, the instantaneous axis ;is at 62 and the tine o con a t t t tansentiai p ane appears as a line:6216.

- face.

. With the distance (54-62) equal to E,

wehave:

lc=EsinA6 The ofiset of the plane 62-15 from the center 541 of the cutter is therefore equal to V c i E cos 0.sin Ai -76.0059 I If we now turn the cutter back through the angle 6, its center will again coincide with 54, a'nd'the offset plane 62-16 will appear as a line 11 inclined at angle to the plane 62-6'l. This ,pl'ane must pass through the point 15, which is the projection of the center 54 to the plane 62'-6|, for it intersects line 54-15 at a distance from 54 equal to its offset 70 cos 6 from the cutter axis divided by cos 0. Its distance is therefore equal to k, which is equal to 54-7 5.

Point 18 is the 'intersectionof the line of contact of the plane 62-15 with the central plane and appears as point 18' after reverse rotation through the angle 0; Its distance from point I5 is equal to the distance from point 18 to the projection of point 541 minus It sin 0 or:

distance (75- 68) (distance 54- 54, sin A6 k sin 0 VNOW'! distance (54-54 sin A5=distance (54-62) sin 0 sin A8 =E sin 0 sin A5 7 =10 sin 0 Hence: 7 V

v distance (7578) =distance (75- 68) This demonstrates that. the straight line'elements pass through the point and intersect the central plane at a constant distance from the point 15, that is, that they lie in a circle centered 'at 15. The straight line elements constitute,

therefore, a conical surface whose axis passes through 15 and is parallel to the cutter axis 54, for the inclination of the straight line elements to the central plane is a constant angle i, see

Fig. 10. 7

Let us now consider point 16' of line, 11 which 7 corresponds to point I6 of line 10 and coincides with point 16 before the described backward rotationof the cutter. Distance 18'l6 equals distance 78-16 which equals distance (68-61) distance (68-18) tan 6, where 5 denotes the'angle 61-59-68 (Fig. 9).

' It is seen from Fig. 9 that: i

distance cs-7s) =E[sin (0-A5) +sin A8] where E is equal to 54-62. It 'isfurther seen that th e distance of the point I5 from the point 18' is equal to: I I

distance (68-67) i-E sin A6- tan 6+ E sin (B-A6) tan 6 i of which only the last member is a variable. I

a The various points 16','which correspond to different turning angles 0, constitute the curve conjugate to the straight line 59-61 of the tooth sur- This curve can be described by a point, which moves along a straight line element of the conical surface centered at 15, while said element rotates on the cone axis 15. Point 16' reaches the the cutting profile 80' has a larger radius filf-Bl a mean distance when iii (Fig. 10) than the curvature radius 6'!-82 of the corresponding tooth profile 66' on account oiithe I blade of'comparatively soft material, which is mounted in the same place as the actual blade. The same relative motions vizj rotation i and lengthwise feed, are then efi'ected between the piece 85 and a finished hardened gear 51,, as take place between the cutter blade and the ear blank during the cutting of a toothspace of the blank. In this way a cutting edge of the desired profile curvature will be formed on the piece 85. The highest accuracy can'be obtained .by going through the process several times after restoring the front face of the piece 85 by grinding or otherwise so that as little deformation aspossible will take place in the final step.

.After having determined the mean profile of the cutting surface, that is, the mean cutting edge, which passes through the point 61, the cutting surface itself can be described by moving this profile along the tangent B5 or 65 (Fig. 10),

as the case may be, while turningthe cutter'cn.

the axis 15 of the above determined conical surface.

Instead of turning the cutter on the axis i5,

itmay also be turned on its own center 54jby moving this center in a circle about the axis 15.

the cutter axis having a center 15 offset a. distance It from the cutter axis 54. The eccentric engages a plane surfaced abutment 84 whose plane engaging surface is parallel ,to' the line The side cutting surface for 'one side of tlie cutter can therefore be described by m'oving'the 50.

cutting profile Bil (Fig. 10), for instance, aleng the tangent 65' as the cutter turns on its center and as its center moves in and out along a straight line parallel to the line 15-68 (Fig.9),

and appearing as the line 54-54,; in :Fig. 13..

determined as E tan 6 [sin (0-A6) +sin At] which is in actuality:

li l i cos i I The end positions of th cutting profiles, at thetime of their out, are shown in Fig. ll. 81 is a blade which cuts at one end of the tooth space and8 8 is a blade which cuts at the other end of the tooth space. Theseblades have side profiles formed by displacing the cutting pro files and 80 along the tangents 55 and 65', respectively. Thus, the centers Bli and 8Iz, respectively, of the profiles Blliand 802 of the same sides of blades8'l and 83 are displaced-parallel to said tangent 65' from the center 8] of the correspondingside profile 80' of the mean blade T= [sin ,(9 A6) sin A6] It. 'ERhe amount of this radial and axial displacement ;is determined as above set :forth by the tooth shapes required on the gear to he .cut.

:Gutters of the-type described have a cylindrical outside cutting surface 89 *(Fig. :12) whichis of varying point-width. The point-width is at its maximum and itsnnlnimum at diametrically opposite points :around the periphery of the cuttej-r, and. the inclination or the cutting profile -.to a plane of rotation 86 of the cutter increases with decreasing poin-t width. FIihus, as :shown in 12, the cutting profile 8-01 of the blade 81, whose tip cutting edge I25 iis of greatest ,-;poi-nt width, has :t-he ieast inclination to said plar-ie of rotation, while the side-cutting edge 302 of the blade '88 whose tip-cutting edge :I2-B 11S of least p int-width, :has the .-greate.$t inclination to said plane The ;point-width --,of the tip -.cutting edge i2?! of theimeanblade 'l-9,'whichcuts at the center of the v'face, is between the maximum and minimum point-widths, and the inclination (of the :sidec'utting edge i8!) of this blade is between the maximum and mini=mum inclinations of the corresponding -side=cutting edges of the blades 81 and 88,. v

*It Willrbfi :noted that the side edges 1802, Stand 80,1 efcrmgobtuse angleswith the tip cutting edges of these 'blades. ltwill be :noted, too, that the point-width :of the blade 8''! in the instance shown is more than twice the pointvidth or the blade 89,. Ordinarily the :largest point-width oi the blades is at least :fiity per cent larger than the smallest point width. Fig. 6 shows a cutter made accordingto described embodiment of the invention in section in development. "lhe d-i-fierent blades of the cutter, which have zbeen heretofore designated generally at id-archers denotedhy th reference numerals 90 to $1.03 inclusive. It will be noted that the blades :98 and 4:09 which are of smallest point-widthsare diametrically opposite the blades Inland. which are ioi-greatestpoint-width. As will be seen from 6-, all ;of the blades have their side surfaces relieved with reference to the surfaces jl 1-8 and H 9 which contain, respectively, the side-cutting edges of all the blades of the cutter. that. is, which constitute the opposite side-cutting surfaces of the :cutter. It will be noted that the side surface and 449 are not true helical surfaces but are slightly concave between their points of maximum and minimum width; This is because of the harmonic 'nature of the cutting motion employed in cutting igears with this cutter and because of making the cutter :to -,conf,or-m to .said motion. p ,12 illustrates the. positions of the profilescf the ,bladesxaa. J9, and ul ;of-the cutter w-hen super imposed upon one another, that is, when rotated into the same radial .plarie of -the cutter. .Since the tip=cutting edgesoi the :bladesare atra constant radial distancedrom the axis of the-cutter. a radial displacement ;8.l1B'-ls.-must be, added geometrically to a displacement 8:l--.8;I-1 "for the center of the blade profile i881 along the tangent 6.5" 11131 order to locate the positions (of theibla'des in the cutter itself; fIPh-is added radial displacement 8'1-8'5. is equal and opposite to -the;,depthwise movementwith respect to line .6 9 per-formed by the cutter I'center during the feed ;of the =cutter iromione end of the blank to the other. In this way. the true center ills-of the profile 8.01 for the position show-1i in Fig. 1'2 can he arrived at. similar manner, :the position 'Blib of :the center of thoiar'ofile iidi canShedet'erin'ined. i Y

'Th'e shape of the cutting edge user may be; de-

termined.byintersmting the cutting surface with the cuttingeface of abl-adewhich:isusually ai -plane face or it can be ascertained bythe xperimental method described withreference to Fig. 8

When the shape of the cutting edges and their distribution about the axis ofthe' cutterihave been determined, there is-sufficient information available .for .making and relieving the cutter on a relievingr machine such ,as described in --m -y U. S. Patent-No..-2,221,8 27 :of November :19, 1940. 0n'e way, in which the side surfaces pf 'the blades of the cutter described 'may be reliefrou-nd, isillustrated in Figs. 14 and :15. The blades .510 are heremountedin a dummy hea'd H0 in positions"tipped forward outof their true-cuttiil positions so that the top surfaces 129 of the blades are ,conoen-tric to the center 1-H of .the dummy head. An eccentrie-I'lZ- whose center is at 1,1,3. is secured tothe spindle '1 H on which the dummy head is mounted, Thiseccentricgis :ar

ra-n -ed to engage .a stationary abutment iii: having-a planeoperativesurface H16. When the dummy heed v i411 isrrotated, theh,.it will-becaused to move back and forth radially along the .line

Mfl-at arrate tor-once per revolution. I

my head, this grinding wheel is ;moved .by :an eccentric or cam a-longitsaxis IZSt-in adirection tangential to the profile 12!. This motion arranged as to repeat once .per revolution of the head. FIT-he opposite side surfaces of 'the;hlades may be similarly relieved *with a wheel 1207. The tops :ofthe blades are ground concentric with theaxis lliLof-the head, that is. while the axis HI stays stationary. I I

in the relieving machine of my U. S..-Patent No. 2,221,825 sbefore mentioned. all of the elements for reliefgrinding thedescribed type 'of :cutter are1-present. All that is required to do is simply to replace the cam 88 ofthis patent by aneccentric,;-;and toholdthe shait'al andrcam afl station ary. :[ihe :cams I55 and 2125 move the grinding wheels axially in one-cycle per. revolutioncf the dummyhead H10. y

-'Iihe cutterdescribedabove'is primarily wroughing cutter for cl'osely approximating a 'given tooth shape. Finishing cutters, which are to be usedin a process employing a harmonic feed motion in thedi-rection of theroot line, can bemade with side-cutting edgeshf uniform circular-arouate zprofilie sh pe :as already described. For finishing, however, the tooth design is preferably adapted to the cutting rocess so that the tooth surface contacts the tangential plane of the-acute ter at mean point :6?! in ,a .slightly concave curve facing the bottom tooth surface. :Inother words; the principles laid down in :my earlier =application No. 360,437 are preferably used ;in {determinmg the tooth shapes off-the .gBfiIS; In such displacement of the cutting profileBO i 10) along the tangent '65 ;is-not apureeha-rmonic motion. It is modified to give the desired curved line or :contact between the tooth surface and the tangential 'plane of the cutter surface. The radial displacement, however, remains (unchanged.

In Fig; "16, I have :shown a modified iorm -of disc milling-cutter constructed according to this invention. This cutter is of segmental form and of the gap type. It comprises a rotary head 2l-30 and a plurality ofeutting segments i3] which are secured to the by bolts or screws 4.32.

In the embodiment shown, the segments are not arranged'all the way around the periphery of the head but there is a peripheral gap, denoted at I33,\between the first segment |3|a and the last segment I3Ib. r T

In the embodiment shown, each' of the se ments comprises four cutting teeth or blades I34. The blades are of successively changing pointwidth but of uniform height and have their tipcutting edges lying in a cylindrical surface I31 coaxial of the cutter axis I36. The roots of the grooves or notches between; the successive teeth of the cutter will then lie in a cylindrical surface I38 also coaxial of the cutter axis I36. Each of V the teeth or blades I34 has a hooked front face and is relieved on its tip surface back of its front face with reference to the cylindrical surface I31 to provide a tip-cutting edge.

The sides of the blades may be straight or curved. When made straight, they are preferably roughed tooth profiles will, of course, be serrated made of zero pressure angle, that is, parallel to one another and parallel to a plane of rotation perpendicular to the axis I36 of the cutter. This construction is illustrated in Fig. 19 where three different blades or cutting teeth of the cutter are shown superimposed on one another and are denoted at 349., I341), and I340, respectively. Opposite side edges of the blade I348. are denoted at I42 and I42, respectively. Opposite side edges of the blade I341; are denoted at MI and MI, respectively. Opposite side edges of the blade 534s are denoted at I40 and I43, respectively. The tipcutting edges of these blades are denoted at I45, I44, and I43,respectively. It will be noted that opposite side edges of the blades are of zero pressure angle, and that the tip-cutting edges are perpendicular to the side edges and parallel to the axis I36 of the cutter. a

- The blades are so arranged around the periphcry of the cutter that'the blade 34a, which is of largest point-width, is first and is followed by blades of progressively decreasing point-width.

In this form of the invention, the blades are so constructed that not only do corresponding sidecutting edges of the blades lie in the same surface but also so that corresponding side surfaces of the blades lie in the same surface. Thus opposite side surfaces of the blades I34 lie in two continuous helical surfaces I41 and I48, respectively, of varying lead. This makes it possible to produce corresponding sides of the blades easily and a'ccuratelywith a continuous cam-controlled motion. Nevertheless the'desired relief on the sides and back of each side-cutting edge willbe obtained.

1 The cutter described can be employed to roughcut spur gears by a process novel with this invention. In this process,the cutter is rotated on its axis in engagement with the spur gear blank to be cut and simultaneously the cutter is fed depthwise into the blank in time with its rotation; This process is illustrated in Figs. 17 and 18. Here 15!) denotes the spur gear to be cut, and I5I and I52 are opposite sides'of a tooth space of this'gean.

space of the blank to the other and its tipedgei I43 travels in a path such as denoted at I54. As

successive blades rotate into cutting position, the cutter is fed continuously depthwise into the,

tooth space to be cut. Thus when the blade I34s has rotated into cutting position, the cutter will: have been fed 'depthwise so that its axis is at I 36".-

' Another form of cutter for cutting spur gears because the sides of the blades are straight and of zero pressure angle. The points of intersec-' tion of the side and tip-cutting edges of the blades will lie, however, in involute curves of the'de'sired shape, and the greater the number of cutting edges, the more closely the roughed toothsurface will approach a smooth involute surface. Any desired tooth shape can be' rough-cut by suitableselection of the point-widthsof succes sive cutting blades. 7

In the process described in connection with Figs. 16 to 20 inclusive it will be seen that the cutter takes a cutwhich is different from the cut taken by conventional milling cutters in the con ventional processof cutting a spur gear. Each blade of a cutter operating in the novel process" described cuts for the full length of the tooth space at all points in the depthwise feed. More over, the blades cut primarily with the tip-cut ting edges and cut straight-profiled chips. The chips are as long as the tooth space and have equal thickness all along their length. This is a most eflicient cutting process.

After a tooth space has been out in the gear blank, the cutter may be withdrawn rapidly from depth. The gap I33 is preferably provided between the first and last blades so that indexing may start during the withdrawal motion without waiting until the cutter has been fully withdrawn frdm the work. A tooth space of theblank may be completed, then, on each revolution of the cutter' and th blank indexed when the gap in the cutter is abreast of the blank.

The blades of the cutter can be relieved in own head and no special relieving motion is required. The side surfaces of the blades can be milled or ground as continuou'ssurfaces as al ready described. The relieved portions'back of the tip-cutting edges may be cut with a milling cutter simultaneously with the cutting of the gashes between successive blades and the relieved portions of the tip surfaces of the blades can be ground with a formed'wheel of circular profile or with a flat wheel. Cutters of this kind can be made very accurately at small cost. Moreover, due to the uniform height of the blades, the cut ter can be readily sharpened. One feature of the cutter disclosed in Figs. 16

to 20 inclusive is that the cutting blades can.

be made to a height considerably less than the height of the tooth space to be cut, thatis, the ashes between successive blades may be considerably less in depth than the depth of the tooth space to be cut. This arrangement permits of providing a maximum number of cutting edges in the cutter.

by rotating the cutter in time with the depthwise feed movement is shown in Figs. 21 and 22. Fig. 22 shows the construction of the blades of this modifiedcutter and Fig. 21"illustrates how 7 it operates in cutting a tooth spacea n In this cutter, the blades are of curved profile..-

having preferably side surfaces which are of cirtheir 1 egsesizca cular arcuate profile shape. In "this cutter, as in the previously described embodiments of the invention, the ti -cutting edges of the blades are at-a mitorm radial distance from the-axis :ar the butter and Vary in @oin't-width around the :pe-

mi'phery of the cutter. The blade fl l, which smallest point width, :has isides it! and tall" which are of least inclination to :a iplan'e of no Ication perpendicular to the axis 16.2 of the outter, while the blade I64, which is 6f i'gre'atest :IJOlIlt-Width, has sides 4&5 and I55 of greatest -inclination to the zplane of rotation; 'llhe blade 8;, which is arranged around the perihheryb f the :cutter intermediate the blades means I,

hassides 1-69 and 1679' which are inclined to the F plane f rotation at angles hater-mediate aing'les of inclination of the sides of the blades still and IGLoespectively. In other words, the in clinations or the correspmrdmg sides of successive blades of the cutter decrease rogressively .ircm like entering lblade- I84 lto last blade loll. corresponding side surtaces of theseblades are preferably relieved back of their side-cuttin edges like the blades :of the cutter of Fig. "23 .hereinaftc'r described.

. ,A cutter made according to Figs. v2l qandz22 may be used in a manner similar to the manner described vreteiience to the cutter of Figs. 1-6 to inclusive; Thus :t-he cutter may be fed depthwise into the blank in time with the rota tion of the cutter. The blade 164 .of v g neatest width begins to out vfirst. As the cutter revolves, it is progressively :f-Bfd into depth, so that when the cutter axis ,has moved vfrom vposition 1-62 to position 1182", the blade L68 will becutting while when the cutter axis has moved to the ,position l:i2"'., the blade KIM will lie-cuttin at full depth position the cutter .is withdrawn engagement with the blank and the blank is indexed. If the cutter is of the slap type, the indexing may be started beiore withdrawal s completed, for it may be started when the sap in the cutter is [abreast of the blank. After indexin the cutter is fed back into on gagement with the blank to cut a new tooth space of the blank. Thus on each revolution of vthe cutter, one tooth space of the blank .H J may beroug'hed out.

The curved side edges of the blades of this cutter do very little side cutting but they serve to produce a smoother Ffinish the ,roughedxtooth sides of the tooth space than will be produced bythe blades of the cutter 16 to 29 inclusive In Fig. 2 1, the cutter s shown as producing toothtprofile shapes l] l and ill on .-op- H posite sides of a tooth ,space :of the gear Hy which approach an involute shape, but it will be obvious that ,any other desired shape may be produced by suitable selection of the pointwidths of successive blades, the profile curtature of the blades, and the inclination of these profiles to the plane .of rotation of -the cuttsr. Like the cutter ,of .Figs. 1.6 to 2.0 inclusive, the cutter of Figs. .21 andv ,22 has blades .of ,uniform height, but usually of ,a height less than thedepth of the toothspaces .to be cut.

Figs. 23 and .25 :show .a cutter similar .to that of .Fig. 22 but made vfor use in cutting Joevel gears, This cutter, like the cutter .of Fig. 22, has blades of uniform height, but usually of less height than the toothspaces of the ,gear to be cut. .Its sides, like .the .sides of the blades of the cutter vof .Fig. 22,, are .of curlled profile, pref erably of circular arcuate profile curvature. Its blades, like the blades of Fig. ,22, are .of varying poirrt m dth arounu the x'rutter 'perichery, and, like the butter of Fig. 522, ithe tio sum edges of this cutter lieiin a cylindrical surface trl'c to the a-xis l fl of the cutter. The sides @115 and N5 of the blade ll-6, which is of least point width, :are least inclined to a plane of rotation of the cutter, while :the sides lT-I and 111 of the blade H28, which is of greatest poi nt width, are most inclined to the axis of the-cutter. blade "9 intermediate the blades 11.6 and I18 :has opposite "side surfaces 18b and I88 whose inclination to the plane of rotation is interme- :diate the inclinations of the sides or the blades 1'16 and H8.

This cutter has its {opposite side-cutting edges lying in surfaces I182 and l'8 3,.respectively, and the side surfaces of the individual blades of this cutter are relieved with reference tothe'se contlnuous surfaces I82 and I83, as clearly shown in ,Fig. .23. In this figure, blades are denoted enerally at 4'84 and their opposite side surfaces at 18-5 and :Hlirespectivcly. e

The cutter of Figs.?23 and 25 may be used in many different ways for cutting bevel gears. i-In the instance illustrated. in 24 the tooth spaces of the gear blank [:95 are :cut by rotating the cutter on its axis and simultanecusly'imparftmg a straight line :feed motion to the cutter longitudinally of the tooth space in time with the cutter rotation and in a direction which is in clined "to the root surface of the tooth space being cut with the result that the matter has E8. combined lengthwise fand deptl'iwise reed move ment as it moves from one :end of the tooth space to theother. Thus in :Fig. :24, :the cutter starts to cut with its axis a position 1&0 and is fed in a direction such that the axis or the cutter moves along the straight line :l-9-l. 5:910 denotes thencsition of the axis of the cutter at the end of the teed movement vand :ISB denotes the position fol the cutter :axis at an intermediate .point in the feed. L92, llfiifgand I82 denote, respectively, the positions of the cutter periphery tor the different nositions I38, I, and '9 of the cutter axis. 1:92 is'al'so the root line of the tooth space being cut, awhile Ill-8 denotes the axis of the blank and l9! its apex.

The feed motion in the instance disclosed may be performed .at "a constant rate (orat "a varying rate. The rateat which the cutter is to be is, of course, reflected the structure 'of the ter.

At the end of the iced movements tooth space of the blank will be completed, and the :cutter then be returned rapidly to .staitting position. The gcutter may be made of the gap ztype and the blank indexed during the return movement mien-the gap :in the cutter is abreast or the blank;

:The process described with reference to Fig. '24 can well be used for finish-cutting providingxfthat the cutter diameter is comparatively large so that the lines of contact between the cutting sur face and the atOOth surface to be produced iex tend su fiiciently lengthwise of the tooth sp ced the instance illustrated, this condition sprev'ails. Here the line. 483 isa line of contact when the cutteris cutting atame'an :point .1394 along the length of the tooth space :and the axis of the cutterjis at and itsperi-phery rat I 92, The line of contact :93 extends overv'o'nly a portion of the height of the tooth surface 1.88 "being cut, each blade of the cutter contacts-with.thexfinished tooth sun-face 498 over only a portion of the height of this surface. l his isv why this cutter can be employed in thecutting of bowel se m.

Each blade is required to finish-cut only a part of the tooth height and each blade therefore may be made of less than the full'tooth height,

I side of'a tooth of the blank at 208. In the feed movement, the cutter axis moves from a starting position 230 to an end position 200'. At the start of the cut,.the cutter periphery is at 202 and at the finish of the cut the periphery of the cutter is at: 202', tangent to the root line 269 of the tooth space being cut at a point 23'! midway-the ends of the tooth space.

The inclined direction of feed is preferred over a straight depthwise feed in the cuttingoi bevel gears for two reasons, namely, improved cutting action and closer approximation of the bevel tooth shape. The improved cutting action is due to the smaller chip-thickness at the start of each cut when the cutter is so fed as to start cutting at the small end of thetooth space. The improved cutting action will be apparent when the spaces of a bevel gearina double-deed cycle.

positionof the periphery of the cutter 202 at the start of a-cut in the process of the present invention is compared with the position 203 which thegperiphery of the cutter would occupy were a pure depthwise feed to be imparted to the cutter and were the initialposition of the cutter axis to be at 204. .It will be seen that the initial cuts taken, where depthwise feed only is employed are shorter and less'eflicient than the cuts taken'initially by a cutter operating according to'the process of this invention. The tooth shape is improved because the upper portion of the desired bevel tooth surface will be out only while the cutter is displaced toward the apex of the blank, that is, while the cutter 'is taking its initial cuts.

. Hence the upper portions of the tooth profile in the method of Fig.26 are cut with'blades of point-width and profile shape suited to produce the desired width and shape of the upper portions of the toothspaces of the blank.

With the embodiment illustrated in Fig. 24, however, it is possible to closely approximate the desired bevel tooth curvature for the whole of the height and length of the tooth surface, but

with the process of Fig. 2 4 the'space has more than natural taper in depth from end to end. In other words, the tangent to the produced root line I92 does'not pass through the gear apex I91. The amount of variation from; actual tooth taper is not great, however, and ;is of the character which has heretofore been generally accepted on small spiralbevel gears. 1

Now while the processes of cutting bevel gears illustrated in. Figs. 24 and 26 have the advantage of simplicity in that a single straight line feed movement is employed, nevertheless greater flexibility in tooth design may be obtained where both lengthwise and depthwise feed movements Here 2l5 denotes the, bevel gearto be cut. 218

is aside of a tooth space of this gear, and 219' the root line of the tooth space.

The cutter employed may be of the type already described with reference to Figs. 23 and 25. The cut starts with the cutter axis in the position 22l3with the cutter periphery at 22! and with the point 223 in the cutter periphery extendingin the direction of the root line 2l9.

.In cutting a tooth space of the gear 5, the

the depth feed ceases but the cutter continuesto be fed in its return movement lengthwise of the tooth'space along the root line 2! until the, point 223 reaches the point 223". Thus the bottom of the tooth space is straightened out. Then the cutter is withdrawn from engagement with the blank and returned to starting position at 223 with its axis at 220. 'During the withdrawal, V the blank is indexed, and, the cycle begins anew to cut a new tooth space of the blank. A gap in the cutter permits of starting indexing while the withdrawal motion is taking place.

During the feed movement of the cutter-"from the position 223 to the position 223', the cutter rotates on its axis through an angle denoted at 226 in Fig. 28. In thereturn feed movement to point 223" the cutter rotates still further min the same direction through an angle 221. During withdrawal and indexing, the cutter will continue to rotate on in the same direction through the angle denotedat 228. The depth-roughing blades of the cutter occupy a portion of its pe-' riphery corresponding to the angle 226. Further blades occupy a portion of periphery corresponding to the angle 221 and straighten out the tooth bottom. A gap in the cutter is provided corresponding'to the angle 228. V

Another cycle of operation, which may be employed in cutting gears according to the present invention on the machine of my earlier application No. 401,631, is illustrated in Figs. 29 and 30.

Here the cut starts with the cutter axis in posi' tion 230 and with the point.233 of the periphery 234 of the cutter extending in'a direction parallel to the root line 232 of a tooth space to be cut in the bevel gear 235. Again the .forward feed movement is along a line 236 inclined at an acute angle to the root line 232 of the tooth space. When the cutter has cut for the full length of the tooth space, it will have reached full depth at point 233'. Then the cutter is fed the full distance back through the tooth space so. that the sides of the tooth space are completely swept over again by the cutter, and in this backward movement, the cutter continues to cut at full depth. When the cutterhas completed the return cut on the tooth space, the cutter is withdrawn from engagement with the blank and moved back to initial position at 233. During this withdrawal'movement, the blank may be indexed. Then the cut begins anew on a'new tooth spaceof the blank. 1 V V In the forward cutting stroke, the cutter will rotate on its axis through an angle 231' (Fig. 30). In the return cutting stroke, thecutter will rotate further on through an angle 238. Indexing will take place while the cutter is rotating still asaaars further on through an angle 239 and. while. the tlon of the side-cuttin s. to a. pl ne QI. r tagap in the cutter is abreast of the blank.

- The depth-roughing blades of a cutter, operating according to the process described in Figs. 29 and 30, are designed to. leave a slight amount. of

stock on the sides of the tooth space for removal by the blades which operate at full depth. A cutter for performing the process illustrated in Figs. 29 and'30 will be. made according to the principles previously described. The inclination of the side-cutting edges. of the blades and their point-width will vary in accordance with the points at which they are to cut. The depthroughing blades-of the cutter could be made. of less'height than the tooth space, but the finishing blades have to be made with side-cutting edges of a height at least. equal to the tooth depth in order to sweep the tooth sides completely in the return stroke at full depth. For this reason ordinarily the roughing blades. are made of the same height as the finishing blades. The tipcutting edges of both roughing and finishing blades will be made concentric of the axis of the cutter as in the previously described forms ofthis invention.

The process illustrated in Fig. 29 is based upon the use of a machine such as disclosed in my earlier application No. 401,631 Where the lengthwise feed movement is a harmonic motion, but it will be obvious that the lengthwise feed movement may be efiected at .a uniform rate or be any other suitable motion. It will iurther be understood that while the process disclosed in Fig. 29 is particularly applicable to the cutting of bevel gears, it may also be applied to. the cutting of spur gears including the finishing of such gears. In the cutting of spur gears, it will be obvious that the-finishing blades will be all of the same profile shape although the point-width of the blades may vary if a localized tooth bearing is to be produced. The point-width ofthe roughing blades will vary in accordance with the principles generally set-forth with regard to Figs. 17 to 22.

Fig. 31 illustrates another possible cycle of operation with this invention. This cycle of operation is similar to that disclosed. with reference to Fig. 2'1. Here thecut starts with the cutter axisv at 240 and the cutter periphery at 244 with the tangent at the po nt 243 of th periphery exending in the direction of the root Line of a tooth space of the gear 2-45 to be cut. The cutter is fed, preferably at a constant rate along a straight line 246, which is inclined at anacute angle to the root line of the 'tooth space, to full depth position Where the periphery of the cutter contacts with the rootline of the tooth space in the point 243'. Then the feed movement'is reversed, and accelerated, and directed along the tooth bottom to point 243", where cutting ceases. The cutter is then. withdrawn from engagement with the blank and returned to initial position 243 whil the blank is indexed. The return feed movement from position 243' tov position 243" serves chiefly to Straighten out the tooth bottom and the whole oithe tooth surface is not swept over a second time.

The cycle of operation illustrated in Fig. 31, like the cycles disclosed in Figs. 17 to 2 8 inclusive, permits of using cutters that have blades .of less height than the depth of the twospaces to .be cut.

Cutters may be employed such as shown in. Figs. 23v and 25. which have blades of varying point-width and in which the inclinas integral with each segment.

tion of thecutter increases with ino easlngzn infiwidth. It is. al p i however. to use a cutter of the. type illustrated in Figs. 16' to 20 inclusive if the operation is a rough, cutting operation only. Even. with the last-mentioned type of cutter, it. is possible to rough tooth. spaces on bevel gears very closely approaching the desired, finished tooth. shape. Only a little extra stock is left at the two ends of the teeth.

The cutters referred to in connectionv with Figs. 16, to 31 inclusive are preferably made, of the segmental type with a plurality of cutting blades A typical segment is shown in Figs. 33 and 34, at 250. This segment. has five integral cutting blades or teeth 25!. The segment has plane sides 252 and, 2753 and a cylindrical inside seating surface 254. The inside surface 254 and the side surface 253 seat against; corresponding urfaces of the utter head 255 and the segment is secured to the cutter head by screws 255 which pass through inclined holes formed in the segment and thread into the cutter head. A key 266 serves to locate the segment angularly on the cutter head.

A cutter may be made up oi several groups of segments Whose bod; portions are of different standard thicknesses. Thus the cutter may comprise segments 25 0 and 2611 (Figs. 34 and 35) The plane side 265 of the segment 250;, however, is at the same distance from the median center line of the cutting portion of this segment 260 as the side 253 of the segment 25,0 is'tro n the center lineof the cutting portion of thatsegmerit. Thus the side surface of a cutter head against. which the sides 253 and 265 of thesegments seat. may be made a single continuous plane. I V

The individual blades of the segments are made according to the principles hereinbefore set .fQ f h. Theyhave their tip-cutting edges arranged at a constant radial distance from the axis of the cutter and are of successively varying; pointwidth. Moreover, if the side profiles of the blades are curved they have preferably uniform curvature, but for. a bevel "gear cutter,..oorrespondingside edges of different blades are ditferently inclined to a plane of rotation of the cutter. Thus, the blade of segment 260, which of the blade of segment253 shownin Fig. 34,. The

side-cutting profile 262 of the blade of segment 26!!v has the same radius of curvature 2B3 as the corresponding side-cutting edge 258 of the blade of segment 253. The center 264 Qfthe profile 262 is displaced, however, with referenc to the center 253 of the profile 25,8.

In Fi as I have shown a segment. 210 for a cutter of; the type illustrated in Figs. 19 and 20. Here the opposite sides 2H and 212 of thecutting portions-of each blade are of zero pressure angle.. n H 7 .32 shows a develope'd view of a segmental cutter made according to this invention This cutter is intended to rotate in the direction of the arrow'2l5. The cutter shown has three segments 216 of relatively large thickness, three segmentsfl'l or medium thickness, and three segments '21s of relatively mau thickness. The thickest segments 216 come first, in the direction of; rotation, of the cutter. Between the last segmeat; :18 and the first segment 216. there is a peripheral gap 219 Tq'illustrate the .changein point-widthof the cutting portions of the sevaxially of thecutter;

'eralsegments'lines 280 and 28! have been drawn.

'These lines contain the points of intersection of the side edges and tip edges of-the cutting teeth of the segments. It will be seen that these lines converge from the first-to the last segment of the a cutter. In the embodiment shown these'lines 280 and 281' are slightly concave in development.

' When segments such-as have been described are employed, a minimum of high speed steel is required in a cutter and the segments can be 'made accurately at low cost. The gashes 282 between successive blades or teeth of the segments and the relieved top surfaces 283 of the blades 7 or teeth of the segments can be milled'simultaneously either by feeding a milling cutter across the widthof the segment from side to side or by feeding it depthwise into the segment. The last named operation is much faster and a larger milling cutter can be used for the purpose.

Segments of various'cutters require no differentiation in the soft state; Where the bladesare 7 to have-curved sides, the cutting portionsof the segments may be made up initially before hardening with chamfered sides. The initial chamfer may be based only on the segment thickness, dif-.

ferent sized segments being differently chamfered. The segments may be hardened, ground on their 7 plane sides and on the cylindrical inside surface,

on-the key way and on their relieved top portions. They may then be put in stock. When an'order is received for a particular cutter, the sidesof the cutting portions of the segments 7 are the only partswhich are required to'be ground; Hence a cutter can be produced on very short notice. The

'grindinlgo'f the sides may be performed on a relieving' grinder of the character-described in my 'earlier Patent No. 2,221,827. Segments of the type disclosed in' Fig. 36 are contemplated-especially for use in cutting gears of finer pitches and, *of course, are left unchamfered. f

a While several difierent' embodiments of the invention have been described, it will 'be under- 'stood thatthe invention-is capableof still furthe r modification. This application is intended to cover any variations, uses, or adaptations of theinvention following; in general, the principles of; the invention and including such departures from the present disclosure as come within known orcustomary practicein the art to Whichthe invention'pertainsandas may be applied to the essential features hereinbefore set'forth and as fall within the scope of the invention or the lim- -it's'of the appended claims.

' --Having thus"described myinvention, what I I curvature'of'the corresponding side cutting edges of successive blades being progressively displaced 2. A rotary gear cutter of the disc type having a plurality bf circumferentially arranged cutting blades whose tip-cutting edges are'arranged at a uniform radial distance from the axis of the cut- '2 ,'s92,27s I I ing blades arranged, on the greater part of its circumference"whichfliave tip and sld'e c'utting edges, the tip-cuttingedgesofsuccessiveblades beingfof successively varying pointy-width and the corresponding" side-cutting" edges of successive blades: being of identical IprofileT'shap'e but; being inclined at different'obtuse angles to the tip cutting "edges of the blades, ithe'iinclination of'corresponding side-cutting edges to the tip Tcutting edgesiincreas'ing with decreasing pointsw'idth;

' '4'. A rotary gear cutteriof. the' "disc type having:

a plurality of circumferentially arranged-blades which have tip and side-cutting edges, the tipcutting edges of successive blades being of successively :varyihg point-width; and the corresponding side-cutting edges of 'successiveblades being diiferently inclined to a plane of rotation.

perpendicular to the axis of "the cutter, the inclinationtof corresponding side-cutting edges to said plane :increasing with. decreasing pointwidth; and diametrically opposite blades having tip-cutting edges of maximum and 'minimum point-width, respectively. r

5; A rotary gear cutter of the disc type'havin'g a plurality of circumferentially arranged blades whose tip-cuttingedges are parallel to the axis of the cutter. and of successively varying :pointwidth andiarearrange'd at a. uniform radial 'dis- ,tance from'said axis and whoselioppositesside profiles are perpendicular to' the tip-cutting edges, said. blades being of uniform-heightand beingof less height'than the height'of the tooth spaces ofthegear'tobecut'.

6. A rotary gear cutter of the disc type having a plurality of' circumferentially arranged blades whose opposite side's ar'e' of circular arcuate profile curvature and'whosetips'cutting edges are of successively varying point -width and are arranged at a uniform radial distance from the axis of the cutter, "corresponding side-cutting edges of successive bladeshavingthe'same radius of curvaturabutivaryinginclination to a plane of! rotation' perpendicular to the axis", of the 7 cutter. 7 r

.of uniform radius of curvature, the centers of L ter'but; are of varying point-width; diametrically opposite blades having'tip -cutting edges of maxi mumlandminimum point-width, respectively; I

" A rotary gear cutter of the 'disc' type hav- 7. 'A rotary gear cutter of-thedisc type having a plurality of 'circumfer'entially arranged blades whose opposite sides are of circular arouate profile curvature and whose tip-cutting edges are of successively varyingpoint-width and are arranged at a uniformradialdistance from the cutter axiscorresponding side-cutting edges of different blades having the-same radius of curvature but varying inclination to a plane of rota- 'tion perpendicular to the axis of the cutter, the

inclination of corresponding side-cutting edges of successive blades'increasing with. decreasing pointf-widt h of the blades r 8. A rotary' 'gear cutter of the disc 'type' having' a plurality of circumferentially arrangedblades Whose opposite sides are of-circular arcuate profile curvature and whose tip-cutting edges are of successively Q varying fpoiht-width; andare I arranged at a 'unifornr-radial' aistaiicerrom the cutter axis, corresponding sid'fcutt'ing edges of different blades having the same iradiusof curve ture but varying inclination to: a a plane of rotation perpendicular to the axis of; the cutter, the

inclination of corresponding side-cutting edges of successive bladesdecreasing with decreasing point-width of the 'blades. i "9.'A rotary gear cutter of the disc type having a a plurality of circumferentially 'arrangedbl ades whose corresponding'sidecutting edges; are such es in i e m dib di l n a cir u a a of a given radius ofcurvaturein a direction inclined to a plane of rotation perpendicular to the axis of the cutter and in a harmonic manner and whose tip-cutting edges are arranged at a constant distance from the axis of the cutter but vary in point-width around the cutter in a harmonic manner.

10. A rotary gear cutter of the disc type having a plurality of circumferentially arranged blades whose tip-cutting edges are of successively varying point-width and are arranged at a constant radial distance from the axis of the cutter, corresponding side surfaces of said blades lying in a continuous helical surface of varying lead.

11. A rotary gear cutter of the disc type, having blades arranged on the greater part of its circumference and having a gap between the last and first blades, the tip-cutting edges of said blades being arranged at a constant distance from the cutter axis and decreasing in point-width from the first to the last blade.

12. A rotary gear cutter of the disc type, having blades arranged on the greater part of its circumference and having a gap between the last and first blades, the tip-cutting edges of said blades being arranged at a constant distance from the cutter axis and decreasing in pointwidth from the first to the last blade, the side edges of said blades being straight and having a constant inclination to the cutter axis.

13. A rotary gear cutter of the disc type having blades arranged on the greater part of its circumference and having a ga between the last and first blade, the tip-cutting edges of said blades being arranged at a constant distance from the cutter axis and decreasing in pointwidth from the first to the last blade, the side edges of said blades being substantially circular arcs and forming obtuse angles with the tip-cutting edges.

'14. A rotary gear cutter of the disc type having a plurality of circumferentially arranged blades which have side and tip cutting edges and which are of uniform height but of less height that the height of the tooth spaces to be cut, the tip cutting edges being arranged at a constant distance from the cutter axis but being of progressively varying point width, and the corresponding side cutting edges 01' different blades being of identical profile shape but differently inclined to their tip cutting edges.

15. A rotary gear cutter of the disc type having a plurality of circumferentially arranged blades which have side and tip cutting edges which are of uniform height but of less height than the height of the tooth spaces to be cut, the tip cutting edges being arranged at a constant distance from the cutter axis but being of progressively varying point width, and corresponding side cutting edges of difierent blades being of identical circular arcuate profile shape but having their centers of curvature displaced axially and radially from one another.

16. A rotary gear cutter of the disc type having a plurality of circumferentially arranged blades which have tip and side cutting edges, the

tip cutting edges of successive blades being arranged at a constant distance from the cutter axis but being of progressively varying point width and the corresponding side cutting edges of successive blades being of identical circular arcuate profile shape but having their centers of curvature displaced axially and radially from one another and diametrically opposite blades having tip cutting edges of maximum and minimum point width, respectively.

17. A rotary gear cutter of the disc type having blades arranged on the greater part of its circumference which have side and tip cutting edges, the tip cutting edges of said blades being arranged at a constant distance from the cutter axis and being of progressively decreasing point width, the side-cutting edges of said blades being straight and having a constant inclination to the cutter axis, corresponding sides of successive blades lying in a common helical surface of varying lead.

18. A rotary cutter of the disc type for cutting tapered gears, having a plurality of equi-spaced cutting blades arranged around its periphery.

which have side and tip cutting edges, the tip cutting edges of said blades being arranged at a constant distance from the axis of the cutter, and successive blades having progressively varying profile shapes, the variation being reversed at diametrically opposite points.

19. A rotary cutter of the disc type for cutting tapered gears, having a plurality of equispaced cutting blades arranged around its periph ery which have side and tip cutting edges, the tip cutting edges of said blades being arranged at a constant distance from the axis of the cutter, and corresponding side cutting edges of successive blades being of identical circular arcuate shape but having their centers of curvature displaced from one another axially and radially of the cutter, the displacement being reversed at diametrically opposite points.

20. A rotary gear cutter of the disc type having blades arranged on the greater part 01' its circumference and having a gap between the last and first blades, the tip-cutting edges of said blades being arranged at a constant distance from the cutter axis and decreasing in point width from the first to the last blade, and the side edges of said blades being substantially circular arcs and forming obtuse angles with the tip-cutting edges of the blades, corresponding side-cutting edges oi the blades being of identical profile curvature but difi'erently inclined to a plane of rotation perpendicular to the. aixs of the cutter.

21. A rotary gear cutter of the disc type having a plurality of cutting blades arranged around its periphery which have side and tip-cutting edges, the tip-cutting edges of the blades being arranged at a constant distance from the axis of the cutter and increasing progressively in pointwidth from the first blade to a blade approximately half way around the periphery of the cutter and then decreasing in point-width again. and corresponding side-cutting edges of the blades being of identical circular arcuate profile shape but having progressively decreasing inclination 

